1. Field of the Invention
This invention relates to an ice heat storage apparatus that uses ice as a thermal storage material and is used for air conditioning of buildings or is used for manufacturing or processing food that will be cooled or refrigerated at ice temperature.
2. Description of the Prior Art
FIG. 1 is a flow sheet showing a prior ice heat storage apparatus described, for example, in "Reito", Vol. 62, No. 715 (May 1982) published by Nihon Reito Kyokai, wherein a refrigerating machine indicated at 1 is equipped with as major constitutional elements a compressor 2, a condenser 3, a decompressing device 4, and an evaporator 5. Reference numeral 6 indicates a thermal storage tank for storing ice and water that serve as thermal storage material, reference numeral 7 indicates a brine piping for a brine such as ethylene glycol, reference numeral 8 indicates a heat transfer tube placed in the thermal storage tank 6, reference numeral 9 indicates a brine pump for circulating the brine, reference numeral 10 indicates chilled water placed in the thermal storage tank, reference numeral 11 indicates ice formed around the heat transfer tube 8, reference numeral 12 indicates a heat exchanger that is a cooling load such as an air handling unit, and reference numeral 13 indicates a chilled water pump for sending the chilled water 10 in the storage tank 6 into the heat exchanger 12.
Now, the operation will be described. The brine that has been cooled by the evaporator 5 of the refrigerating machine 1 to about -10.degree. C. is sent to the heat transfer tube 8 through the brine piping 7, and during the passage of the brine through the heat transfer tube 8, the water surrounding it is cooled. Part of water cooled to the freezing point or below freezes around the heat transfer tube 8 and forms ice 11. The brine which has exchanged heat with the chilled water 10 and whose temperature has risen is brought back to the evaporator 5 by the brine pump 9 so that it may be circulated.
The cooling operation by the above action is carried out at midnight when the electric charges are low, so that ice and water having a temperature of 0.degree. C. are stored in the thermal storage tank 6. Generally, 40 to 50% of the total amount of the chilled water in the thermal storage tank 6 are stored as ice. Since the latent heat of ice is about 80 kcal/kg, which is about 80 times as high as the specific heat of water, ice can store a quantity of heat 32 to 40 times as large as the case wherein thermal storage is carried out using water having a temperature of 0.degree. C. During the daytime, the chilled water in the thermal storage tank 6 is sent to the heat exchanger 12 by the chilled water pump 13, the temperature of the chilled water rises because it has cooled the cooling load, and it is brought back to the thermal storage tank 6. The ice in the thermal storage tank 6 melts gradually, and it gives its latent heat to the cooling load. Arrows in the figure indicate the directions of the flows of the fluids. Since the operation of the refrigerating machine 1 itself is the same as that of usual one, the description thereof is omitted.
Since the prior ice thermal storage apparatus is constituted as described above, a brine having a temperature of about -10.degree. C. is required to form ice, and it is needed to operate the refrigerating machine 1 in a low evaporating temperature range low in coefficient of performance. Further, as an ice layer grows around the heat transfer tube 8, the heat resistance between the brine and the chilled water becomes great, and since the brine temperature lowers, the coefficient of performance of the refrigerating machine 1 lowers further, and the power consumption increases. Furthermore, since it is needed that the heat transfer tube 8 of a material that is good in heat conductivity and expensive is placed in the thermal storage tank 6, the manufacturing cost of the thermal storage tank 6 becomes high. In the prior art, there was, for example, such a problem that when ice adhered around the heat transfer tube 8, it was feared that the expansion of the volume at the time of the solidification would damage the thermal storage tank 6 or the heat transfer tube 8, so that the rate of formation of ice in the thermal storage tank 6 had to be suppressed to about 50%.